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JEE Physics Solved Question Paper 2007

Multiple Choice Questions

61.
When a monochromatic point source of light is at a distance 0.2 m from a photoelectric cell, the saturation current and cut-off voltage are 12.0 mA and 0.5 V. If the same source is placed 0.4 m away from the photoelectric cell, then the saturation current and the stopping potential respectively are

4 mA and 1 V

12 mA and 1 V

3 mA and 0.5 V

12 mA and 0.5 V

3 mA and 0.5 V

The cut-off voltage or stopping potential measure maximum kinetic energy of the electron. It depends on the frequency of incident light whereas the current depends on the number of photons incident. Hence, cut-off voltage will be 0.5 V. Now by inverse square law,

$12 \propto \frac{1}{{(0.2)}^{2}} or I \propto \frac{1}{{(0.4)}^{2}} ∴ \frac{I}{12} = \frac{{(0.2)}^{2}}{{(0.4)}^{2}} = \frac{1}{4} or I = \frac{12}{4} = 3 mA$

62.

Consider the nuclear reaction X²⁰⁰ → A¹¹⁰ + B⁸⁰, If the binding energy per nucleon for X, A and B are 7.4 MeV, 8.2 MeV and 8.1 MeV respectively, then the energy released in the reaction is

70 MeV
200 MeV
190 MeV
10 MeV

63.

The natural boron of atomic weight 10.81 is found to have two isotopes B¹⁰ and B¹¹. The ratio of abundance of isotopes in natural boron should be

11 : 10
81 : 19
19 : 81
15 : 16

64.

Radium has a half-life of 5 yr. The probability of decay of a radium nucleus in 10 yr is

50 %
75 %
100 %
60 %

65.

When the forward bias voltage of a diode is changed from 0.6 V to 0.7 V, the current changes from 5 mA to 15 mA. Then its forward bias resistance is

0.01 Ω
0.1 Ω
10 Ω
100 Ω

66.

In common emitter amplifier, the current gain is 62. The collector resistance and input resistance are 5 kΩ and 500 Ω respectively. If the input voltage is 0.1 V, the output voltage is

0.61 V
6.2 V
62 V
620 V

67.

The current gain of a transistor in common base mode is 0.995. The current gain of the same transistor in common emitter mode is

68.

The real time variation of input signals A and B are as shown below. If the inputs are fed into NAND gate, then select the output signal from the following